Democratic presidential nominee Hillary Clinton cancelled two days of campaigning after falling ill, inserting new speculation about her health into a presidential campaign in which Republican Donald Trump has called her weak and unfit.

Clinton fell ill yesterday (Sunday local time) during a memorial service in New York marking the 15th anniversary of the September 11, 2001, terrorist attacks, leaving abruptly. Video of Clinton's hurried departure from the Ground Zero memorial showed her buckling and stumbling as she got into her van.

Clinton's campaign later issued a statement from her doctor revealing that she had been diagnosed with pneumonia two days earlier.

The video, circulated on Twitter, appeared to show Clinton, 68, flanked by several Secret Service agents, leaning against a security bollard while agents prepare to assist her into a black van. As she steps forward, Clinton can be seen falling as agents help lift her into the van.


"Secretary Clinton has been experiencing a cough related to allergies," Lisa R Bardack, Clinton's physician, said yesterday. "On Friday, during follow-up evaluation of her prolonged cough, she was diagnosed with pneumonia. She was put on antibiotics, and advised to rest and modify her schedule. While at this morning's event, she became overheated and dehydrated. I have just examined her and she is now re-hydrated and recovering nicely."

A planned trip to California today and tomorrow has been cancelled, campaign officials said yesterday. Clinton had been scheduled to attend several fundraising events across the state, in addition to a major economic speech in Southern California and a taped appearance on the talk show Ellen. It remained uncertain whether Clinton would continue with her planned travel to Las Vegas on Thursday.

Campaign spokesman Nick Merrill said Clinton left the ceremony early and retreated to her daughter Chelsea's apartment in the Gramercy neighbourhood of Lower Manhattan.

Clinton was not seen for more than two hours, after which she emerged from Chelsea Clinton's apartment building, walking normally, smiling and waving.

The incident quickly renewed attention to Clinton's health. Trump has repeatedly questioned her wellbeing, saying that she doesn't have the "strength" or "stamina" for the presidency and accusing her of being "exhausted" and sleeping too much.

A coughing episode on Labour Day had prompted a fresh round of questions about Clinton's health. During a speech at a festival in Cleveland, Clinton started coughing repeatedly at the outset of her remarks, took several sips of water and a lozenge and continued to sound hoarse as she spoke. Later that day, Clinton told reporters her condition was caused by "seasonal allergies". An initial campaign statement about yesterday's illness did not mention the pneumonia diagnosis from two days prior, adding to public speculation that the campaign was hiding something. Clinton has followed an intensely busy schedule in recent days, and she had appeared healthy when she convened a meeting of national security experts on Saturday in New York and then spoke at a fundraising party that night. It was at that fundraiser where Clinton ignited a controversy by claiming that "half" of Trump's supporters are in a "basket of deplorables". Neither Trump, who is 70, nor his aides responded to requests for comment yesterday; nor did he weigh in on Twitter or in television interviews, as he is known to do. But attacks from him and his allies, including former New York Mayor Rudolph Giuliani, have intensified in the past month as unverified and often debunked theories about Clinton's health have floated on the internet. And yesterday's incident prompted an avalanche of speculation on social media from other Clinton critics.

According to two Trump advisers, Trump decided to stay away from seizing on yesterday's incident with the aim of bringing Clinton's "deplorables" comments - for which she has expressed regret - back to the forefront of the campaign this week and avoiding any chance for Clinton to say that Trump was overstepping on the health front.

If confronted by reporters about Clinton's health, Trump plans to say that he hopes she gets well and may raise questions about the campaign's transparency, they added.

Both Clinton and Trump had planned to take the day off from formal campaigning in observance of the September 11 anniversary. Trump attended the same memorial service at Ground Zero.

Peter King, a Long Island congressman who stood with Trump's group at the ceremony, said he spoke with Trump shortly after Clinton departed.

"It was actually Trump who told me what was going on," King said. "He leaned over and told me that 'Hillary wasn't feeling well'. I said, 'Really'? That was all he said."

A former Secret Service agent said that the security detail's movements showed that the agents had not planned for her to leave that early and had to make some rushed security plans on the fly. Clinton's van was not in place when she arrived at the kerb, and her detail leader, who normally sticks by her side at all times, had to leave her momentarily to open the door of her van.

A small group of reporters travelling with Clinton was left behind and was not immediately informed that she had departed.

As Clinton exited her daughter's apartment building, she hugged a young girl and posed for a picture, waved and briefly answered questions shouted by reporters before she departed in her motorcade.

"I'm feeling great, it's a beautiful day in New York," Clinton said.

Clinton has been generally healthy, with the exception of clotting in one leg in 1998 and a concussion and associated health problems from a fall in December 2012. But she has been attacked repeatedly by critics and accused of hiding more serious health issues.

Giuliani, a close adviser to Trump who is regularly at his side on the campaign trail, said last month that he thinks Clinton is "tired" and "looks sick". "What you've got to do is go online," Giuliani said on Fox News Sunday last month, accusing the media of hiding information about Clinton's health. "So, go online and put down 'Hillary Clinton illness', take a look at the videos for yourself."